A vehicle body frame in a saddle ride type vehicle, such as a four-wheel buggy car, generally includes a main frame and a rear frame composed of a left-right pair of pipe members. The main frame on the vehicle body front side typically supports an engine and the rear frame typically includes seat rails for supporting a seat on the rear side of the main frame. Japanese Patent Laid-open No. 2000-33894 discloses such an apparatus.
In the above-mentioned vehicle body frame structure, often a heavy body, such as an exhaust muffler, a battery, etc., is supported on the side of either one of the left-right pair of rear frames. Supporting such a heavy body may generate resonance between the left-right pair of pipe members, because the vibration modes in the left and right rear frames are different.
In order to minimize or prevent the resonance from being generated, it may be contemplated to adopt a structure in which the left and right pipe members are different in diametric size so that they have a different modulus of section.
When such a structure is adopted, however, it is important not to spoil the appearance quality. Further, in the case of assembling the rear frames by thus using the pipe members with different diametric sizes on the left and right sides, the mount portions of mount component parts or connection component parts are different between the left and right sides. As a result, the assembly process is likely to be complicated.
Thus, there is a need in the industry to provide a vehicle body frame structure which minimizes or prevents the generation of resonance, while maintaining the appearance quality of the structure and enhancing the design for assembly of the structure.